Self-injection locked laser device and molecular information output device

Abstract

Provided is a self-injection locked laser device in which environmental changes are less likely to occur and variations in the optical path length and the resonator length are reduced. The self-injection locked laser device comprises: a first base plate; a second base plate; a temperature adjusting element disposed between the first base plate and the second base plate; a semiconductor laser light source disposed on the first base plate; a reference resonator that is disposed on the first base plate, that is positioned along the optical path of laser light emitted from the semiconductor laser light source, that is provided with at least a first mirror and a second mirror, and that provides the semiconductor laser light source with optical feedback; a first cover that covers the semiconductor laser light source and the reference resonator and that contacts the first base plate; and a second cover that covers the first cover and that contacts the second base plate.

Description

Self-injection-locked laser device and molecular information output device

[0001] The present disclosure relates to a self-injection-locked laser device and a molecular information output device.

[0002] For example, Patent Document 1 discloses an optical module that has a semiconductor laser element and a housing, and that locks the wavelength of laser light emitted from the semiconductor laser element.

[0003] JP 2012-68407 A

[0004] An object of an embodiment of the present disclosure is to provide a self-injection locked laser device that is less susceptible to environmental changes and in which fluctuations in the optical path length and the resonator length are reduced.

[0005] A self-injection locked laser device according to an embodiment of the present disclosure includes a first base plate, a second base plate, a temperature adjustment element disposed between the first base plate and the second base plate, a semiconductor laser light source disposed on the first base plate, a reference resonator disposed on the first base plate, positioned in an optical path of laser light emitted from the semiconductor laser light source, including at least a first mirror and a second mirror, and providing optical feedback to the semiconductor laser light source, a first cover covering the semiconductor laser light source and the reference resonator and in contact with the first base plate, and a second cover covering the first cover and in contact with the second base plate.

[0006] A self-injection locked laser device according to another embodiment of the present disclosure includes a first substrate including a recess, a second substrate, a temperature adjustment element disposed between the first substrate and the second substrate, a semiconductor laser light source disposed in the recess of the first substrate, a reference resonator disposed in the recess of the first substrate, positioned in an optical path of laser light emitted from the semiconductor laser light source, including at least a first mirror and a second mirror, and providing optical feedback to the semiconductor laser light source, a first cover covering the semiconductor laser light source and the reference resonator and in contact with the first substrate, and a second cover covering the first cover and in contact with the second substrate.

[0007] According to an embodiment of the present disclosure, it is possible to provide a self-injection locked laser device that is less susceptible to environmental changes and in which fluctuations in the optical path length and the cavity length are reduced.

[0008] 1 is a schematic top view of a self-injection locked laser device according to a first embodiment. FIG. 1 is a schematic cross-sectional view taken along line II-II in FIG. 1. FIG. 2 is a schematic cross-sectional view taken along line IIIA-IIIA in FIG. 1. FIG. 3 is a block diagram showing the hardware configuration of a control unit included in the self-injection locked laser device according to the first embodiment. FIG. 4 is a block diagram showing the functional configuration of the control unit included in the self-injection locked laser device according to the first embodiment. FIG. 5 is a flowchart showing processing by the control unit included in the self-injection locked laser device according to the first embodiment. FIG. 6 is a schematic top view of a self-injection locked laser device according to a second embodiment. FIG. 7 is a schematic cross-sectional view taken along line V-V in FIG. 4. FIG. 8 is a schematic top view of a first example of a self-injection locked laser device according to a third embodiment. FIG. 9 is a schematic cross-sectional view of a self-injection locked laser device according to a second embodiment. FIG. 10 is a schematic top view of a self-injection locked laser device according to a first modification. FIG. 11 is a schematic cross-sectional view of a molecular information output device according to a fourth embodiment.

[0009] A self-injection locked laser device and a molecular information output device according to embodiments of the present disclosure will be described in detail with reference to the drawings. However, the following embodiments are merely examples of a self-injection locked laser device and a molecular information output device for realizing the technical concept of the present disclosure, and are not limited to the following. Hereinafter, the self-injection locked laser device will be abbreviated as a SIL-LD device.

[0010] Furthermore, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, etc. of components described in the embodiments are not intended to limit the scope of the present disclosure, but are merely illustrative examples. Since each drawing is a schematic representation of an embodiment, the scale, spacing, or positional relationship of each component may be exaggerated, or some components may be omitted. In the following description, the same names and symbols indicate the same or similar components, and detailed descriptions will be omitted as appropriate. Cross-sectional views may be used in which only the cut surface is shown.

[0011] In each drawing, directions are represented using a Cartesian coordinate system having an X-axis, a Y-axis, and a Z-axis. The X-axis, the Y-axis, and the Z-axis are perpendicular to one another. The direction in which an arrow points in the X-axis is denoted as the +X-axis, and the direction opposite to the +X-axis is denoted as the -X-axis. The direction in which an arrow points in the Y-axis is denoted as the +Y-axis, and the direction opposite to the +Y-axis is denoted as the -Y-axis. The direction in which an arrow points in the Z-axis is denoted as the +Z-axis, and the direction opposite to the +Z-axis is denoted as the -Z-axis. However, these do not limit the orientation of the SIL-LD device and molecular information output device according to the embodiment during use, and the orientation of the SIL-LD device and molecular information output device according to the embodiment may be arbitrary.

[0012] The term "top view" in the embodiments refers to a view of an object viewed from the +Z direction. In the description of the embodiments, a top view showing the inside of a first cover and a second cover of the SIL-LD device may be shown in order to explain the internal configuration of the SIL-LD device according to the embodiments. In the embodiments described below, "along the X-axis, Y-axis, and Z-axis" includes an object having an inclination within a range of ±15°, ±10°, or preferably ±5° with respect to these axes. In this specification, the positional relationship expressed as "above" includes both a case where the object is in contact with the object and a case where the object is positioned above the object but not in contact with the object.

[0013] [First Embodiment] <Configuration of SIL-LD Device According to First Embodiment> The SIL-LD device according to the first embodiment will be described with reference to FIGS. 1 to 3A. FIG. 1 is a schematic top view showing an example of a SIL-LD device 100 according to the first embodiment. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1. FIG. 3A is a schematic cross-sectional view taken along line IIIA-IIIA in FIG. 1. Note that in FIGS. 1 to 3A, arrows indicate portions of the laser beams M1 to M6 passing through the interior of the SIL-LD device 100. Also, in FIGS. 1 to 3A, a broken line indicates an optical path P along which the laser beams M1 to M6 pass within the SIL-LD device 100.

[0014] 1 to 3A, the SIL-LD device 100 includes a first base plate 1, a second base plate 2, a temperature adjustment element 3 disposed between the first base plate 1 and the second base plate 2, and a semiconductor laser light source 4 disposed on the first base plate 1. The SIL-LD device 100 also includes a reference resonator 5 disposed on the first base plate 1, located in an optical path P of laser light M1 emitted from the semiconductor laser light source 4, including at least a first mirror 51 and a second mirror 52, and providing optical feedback to the semiconductor laser light source 4. The SIL-LD device 100 further includes a first cover 7 that covers the semiconductor laser light source 4 and the reference resonator 5 and is in contact with the first base plate 1, and a second cover 8 that covers the first cover 7 and is in contact with the second base plate 2.

[0015] 1 to 3A, the SIL-LD device 100 includes a first collimating lens 9 that transmits laser light M1 emitted from the semiconductor laser light source 4, and a beam splitter 10 that transmits a portion of the laser light M1 that has passed through the first collimating lens 9 and reflects the remainder of the laser light M1. Also, in the example shown in FIGS. 1 to 3A, the SIL-LD device 100 includes an optical isolator 11 located between the first cover 7 and the second cover 8 and on the optical path P, and a condenser lens 12 that transmits laser light M3 reflected by the beam splitter 10. Also, in the example shown in FIG. 2, a temperature sensor 13 is embedded in the first base plate 1. Also, in the example shown in FIG. 2, the SIL-LD device 100 may further include a position adjustment element 21 that moves the beam splitter 10.

[0016] In the example shown in FIG. 1 , laser light M3 is reflected by the beam splitter 10 and then transmitted through the condenser lens 12, and is incident on the reference resonator 5. The laser light M3 incident on the reference resonator 5 is reflected by each of the first mirror 51 and the second mirror 52, and resonates while traveling back and forth between the first mirror 51 and the second mirror 52. The arrow indicating the laser light M4 in FIG. 1 represents the laser light traveling back and forth between the first mirror 51 and the second mirror 52. A portion of the laser light M4 is emitted from the reference resonator 5 in the direction where the condenser lens 12 is located while traveling back and forth between the first mirror 51 and the second mirror 52. The laser light M5 emitted from the reference resonator 5 is transmitted through the condenser lens 12 and is then incident on the beam splitter 10. A portion of the laser light M5 incident on the beam splitter 10 is reflected by the beam splitter 10 in the direction where the semiconductor laser light source 4 is located. Laser light M6, which is a part of the laser light M5 reflected by the beam splitter 10, passes through the first collimator lens 9 and then enters the semiconductor laser light source 4, where it applies feedback to the optical frequency of the laser light M1.

[0017] When the difference between the optical frequency of the laser light M1 emitted from the semiconductor laser light source 4 and the resonant frequency of the reference resonator 5, which is determined according to the resonator length Lc of the reference resonator 5, approaches approximately equal to or less than the full width at half maximum of the linewidth of the reference resonator 5, the laser light M1 enters the reference resonator 5 and travels back and forth, thereby filtering the optical frequency. The filtered light, which has a narrower linewidth than its original linewidth, is fed back to the semiconductor laser light source 4. As a result of the optical feedback, the laser light M1 exhibits a linewidth narrowing effect due to self-injection locking. The linewidth of the self-injection locked laser light may be, for example, 500 Hz or more and 1 MHz or less. The oscillation frequency of the self-injection locked laser light approximately matches the resonant frequency of the reference resonator 5. Note that when there is a large difference between the optical frequency of the laser light M1 emitted from the semiconductor laser light source 4 and the resonant frequency of the reference resonator 5, the linewidth of the laser light Mo extracted from the SIL-LD device 100 becomes equal to the linewidth of the laser light M1 emitted from the semiconductor laser light source 4. This is because self-injection locking does not occur since the laser light M1 emitted from the semiconductor laser light source 4 does not resonate with the reference resonator 5. In this case, the linewidth of the laser light Mo extracted from the SIL-LD device 100 is not narrower than the linewidth of the laser light M1.

[0018] In order to narrow the linewidth of the laser beam Mo extracted from the SIL-LD device 100, the optical path length Lb between the first end face 41 of the semiconductor laser element 401 of the semiconductor laser light source 4 and the first surface 511 of the reference resonator 5 must be λ×(N+θ) / 2, and the resonator length Lc of the reference resonator 5 must be λ×M / 2. The optical path length Lb represents the length of the optical feedback path in self-injection locking. In FIG. 1 , the sum of Lb1 and Lb2 corresponds to Lb. Here, λ is the wavelength of the laser beam Mo, N and M are positive integers, and θ is a constant specific to the semiconductor laser element 401. However, if at least one of the optical path length Lb and the resonator length Lc changes by approximately λ / 2 due to environmental changes such as temperature, air pressure, humidity, or convection, the above condition is not met, and the linewidth of the laser beam Mo will not be narrowed.

[0019] In this embodiment, the first base plate 1 and the first cover 7 protect the semiconductor laser light source 4 and the reference resonator 5 from environmental changes within the SIL-LD device 100, thereby reducing fluctuations in the optical path length Lb and the resonator length Lc. This makes it possible to stabilize the state in which the linewidth of the laser light Mo is narrowed by self-injection locking. Furthermore, the operation of the temperature adjustment element 3 is controlled based on the temperature of the semiconductor laser light source 4 detected by the temperature sensor 13. The temperature of the first base plate 1 is kept constant, and the temperature of the first cover 7 in contact with the first base plate 1 also approaches the temperature of the first base plate 1. Therefore, the semiconductor laser light source 4 and the reference resonator 5, which are surrounded by the first base plate 1 and the first cover 7, are less susceptible to environmental changes, and fluctuations in the optical path length Lb and the resonator length Lc can be reduced.

[0020] Each element constituting the SIL-LD device 100 will be described in detail below.

[0021] 1 to 3A, the first base plate 1 is disposed on the second base plate 2 via the temperature adjustment element 3. However, as long as the temperature adjustment element 3 is disposed between the first base plate 1 and the second base plate 2, the positional relationship between the first base plate 1 and the second base plate 2 may be arbitrary. The first base plate 1 may be disposed next to the second base plate 2 in either the X direction or the Y direction via the temperature adjustment element 3.

[0022] The material of the first base plate 1 and the second base plate 2 may include at least one selected from the group consisting of aluminum, copper, graphite, diamond, aluminum nitride, Super Invar, and low-thermal expansion glass. When the material of the first base plate 1 and the second base plate 2 is aluminum, copper, graphite, diamond, or aluminum nitride, heat dissipation from the base plate can be improved. Furthermore, when the material of the first base plate 1 and the second base plate 2 is Super Invar or low-thermal expansion glass, fluctuations in the optical path length Lb and the resonator length Lc due to thermal expansion can be reduced. The materials of the first base plate 1 and the second base plate 2 may be the same or different. In the SIL-LD device 100, it is preferable that the first base plate 1 is made of a material with low thermal expansion and the second base plate 2 is made of a material with high thermal conductivity. This allows efficient heat dissipation by the second base plate 2, making it easy to maintain a constant temperature of the first base plate 1. Furthermore, when the temperature of the first base plate 1 is kept constant, fluctuations in the optical path length Lb are reduced due to the small thermal expansion of the first base plate 1. The combination of the first base plate 1 and the second base plate 2 may be, for example, such that the first base plate 1 is made of Super Invar and the second base plate 2 is made of copper.

[0023] (Temperature Adjustment Element 3) The temperature adjustment element 3 is disposed between the first base plate 1 and the second base plate 2. The temperature adjustment element 3 is bonded to each of the first base plate 1 and the second base plate 2, for example, via an adhesive. The adhesive may be, for example, thermal grease. In the example shown in FIGS. 1 to 3A, the temperature adjustment element 3 includes a Peltier element. The temperature of the first base plate 1 is maintained constant by adjusting the temperature of the first base plate 1 using the Peltier element. Here, "maintaining a constant temperature" means that the temperature of the first base plate 1 fluctuates within a range of ±1°C, preferably ±0.01°C, or more preferably ±0.001°C relative to a predetermined temperature. However, the temperature adjustment element 3 is not limited to a Peltier element, as long as it is disposed between the first base plate 1 and the second base plate 2 and is capable of temperature adjustment. The SIL-LD device 100 can reduce fluctuations in the optical path length Lb associated with thermal expansion of the first base plate 1 by reducing the temperature rise of the first base plate 1 using the temperature adjustment element 3. Furthermore, by keeping the temperature of the first base plate constant, it is possible to reduce expansion or contraction of the reference resonator 5 and reduce fluctuations in the resonator length Lc. The temperature adjustment element 3 may be arranged so as to overlap the semiconductor laser light source 4 and the reference resonator 5 in a top view. In this way, by keeping the temperature of the first base plate 1 constant, it is possible to reduce temperature changes in the semiconductor laser light source 4 and the reference resonator 5.

[0024] (Semiconductor Laser Light Source 4) In the example shown in FIG. 1 , the semiconductor laser light source 4 includes a semiconductor laser element 401 and a package 402 that seals the semiconductor laser element 401. A submount may further be provided between the semiconductor laser element and the package. The inside of the package 402 is sealed with dry air or an inert gas. This reduces the possibility of light dust collection and reduces deterioration of the semiconductor laser element 401. The shorter the oscillation wavelength of the semiconductor laser element 401 is, for example, 550 nm or less, 500 nm or less, or 450 nm or less, the more preferably the inside of the package 402 is sealed. This is because the optical energy density at the first facet 41 of the semiconductor laser element 401 increases.

[0025] The semiconductor laser element 401 includes a first end facet 41 and a second end facet 42. The semiconductor laser element 401 emits laser light M1 from the first end facet 41. The wavelength band of the laser light M1 emitted from the semiconductor laser element 401 is, for example, 360 nm to 1600 nm, preferably 400 nm to 550 nm. The linewidth (frequency) of the laser light M1 emitted solely from the semiconductor laser element 401 is, for example, 10 MHz to 1 GHz. The linewidth value is not limited to this example and may be smaller than 10 MHz. Self-injection locking can further reduce the linewidth of the light extracted from the SIL-LD device 100. The SIL-LD device 100 shown in FIG. 1 has a configuration in which self-injection locking and light extraction are performed on the side where the first end facet 41 of the semiconductor laser element 401 is located.

[0026] 1 to 3A, the semiconductor laser light source 4 includes a distributed feedback laser diode (DFB-LD) element. By including the DFB-LD element in the semiconductor laser light source 4, the laser light M1 emitted from the semiconductor laser light source 4 has a single frequency, and the laser light Mo extracted from the SIL-LD device 100 can also have a single frequency and a narrow linewidth.

[0027] The DFB-LD element can be configured to include a material of a III-V group element or the like. The DFB-LD element may be, for example, a nitride semiconductor, an arsenide semiconductor, or a phosphide semiconductor. The DFB-LD element is, for example, a laminate having an n-side cladding layer, an n-side optical guide layer, an active layer, a p-side optical guide layer, and a p-side cladding layer, and an optical waveguide is formed therein. Either the n-side cladding layer or the n-side optical guide layer includes at least one n-type semiconductor layer. The active layer may be a quantum well. Either the p-side optical guide layer or the p-side cladding layer includes at least one p-type semiconductor layer. The DFB-LD element may have a diffraction grating in at least a part of the waveguide. The period of the diffraction grating is λ / (2×n ｅｑ ) where λ is the oscillation wavelength of the laser light M1 of the semiconductor laser element, and n ｅｑ is the equivalent refractive index. In this example, the order is 1.

[0028] 1 to 3A, the first end face 41 of the DFB-LD element is coated with an anti-reflection film 410. The reflectivity of the anti-reflection film 410 with respect to the wavelength of the laser light may be, for example, 0.01% or more and 1% or less. By coating the end face with the anti-reflection film 410, the DFB-LD element can obtain stable single-mode characteristics. The second end face 42 is coated with a high-reflection film 420. The reflectivity of the high-reflection film with respect to the wavelength of the laser light may be, for example, 90% or more and 99.9% or less.

[0029] 1 to 3A, the diffraction grating of the DFB-LD element has a λ / 4 phase shift structure. A λ / 4 phase shift structure refers to a structure in which the phase of the diffraction grating provided in the DFB-LD element is shifted corresponding to, for example, ¼ of the peak wavelength of the laser light emitted from the DFB-LD element. By having the λ / 4 phase shift structure, the DFB-LD element can obtain stable single-mode characteristics.

[0030] The semiconductor laser light source 4 is not limited to a DFB-LD element. For example, the semiconductor laser light source 4 may include a semiconductor laser element other than a DFB-LD element. For example, the semiconductor laser light source 4 may include a distributed Bragg reflector (DBR) laser element or a photonic crystal surface-emitting laser (PCSEL).

[0031] (Reference Resonator 5) In the reference resonator 5 shown in FIG. 1 , the first mirror 51 includes a first surface 511, which is a light-reflecting surface of the reference resonator 5, and a second surface 512 located on the opposite side of the first surface 511. The second mirror 52 includes a third surface 513 facing the first surface 511 and a fourth surface 514 located on the opposite side of the third surface 513. The third surface 513 is a light-reflecting surface of the reference resonator 5. The reflectance of the first mirror 51 with respect to the wavelength of the laser light M1 emitted from the semiconductor laser light source 4 is, for example, 95.0% or more and 99.9% or less. The reflectance of the second mirror 52 with respect to the wavelength of the laser light M1 emitted from the semiconductor laser light source 4 is, for example, 95.0% or more and 99.9% or less. The first mirror 51 and the second mirror 52 in the reference resonator 5 can be configured using a material such as synthetic quartz or low-thermal expansion glass.

[0032] The resonator length Lc of the reference resonator 5 corresponds to the distance between the first mirror 51 and the second mirror 52. More specifically, in the example shown in FIG. 1 , the resonator length Lc of the reference resonator 5 corresponds to the distance between the first surface 511 of the first mirror 51 and the third surface 513 of the second mirror 52. The resonator length Lc is, for example, 10 mm, but is not limited to this. It can be changed as appropriate depending on the desired frequency of the laser light Mo. The reference resonator 5 shown in FIG. 1 is slightly tilted with respect to the optical axis of the laser light M3. This makes it difficult for light reflected by the second surface 512 of the first mirror 51 to return to the semiconductor laser light source 4 as return light. In FIG. 1 , since the reference resonator 5 is tilted, light resonating with the reference resonator 5 resonates along a V-shaped optical path.

[0033] In the reference resonator 5 shown in FIGS. 1 to 3A, the first mirror 51 and the second mirror 52 are each a concave mirror. In the example shown in FIGS. 1 to 3A, the first mirror 51 and the second mirror 52 form a confocal resonator. That is, the radii of curvature of the first mirror 51 and the second mirror 52 are equal, and the distance between the first mirror 51 and the second mirror 52 is equal to the magnitude of the radii of curvature. As a result, the fundamental mode and higher-order modes that resonate in the reference resonator 5 are degenerated and resonate at the same frequency. A confocal resonator has a simple spectral structure due to mode degeneracy. Furthermore, the mode of light extracted from the reference resonator 5 depends on the mode of light resonating with the reference resonator 5. Therefore, if fundamental-mode laser light is resonated in the reference resonator 5, fundamental-mode light is extracted and fed back to the semiconductor laser element 401. Therefore, the confocal resonator is suitable for mode observation of the laser light Mo extracted from the SIL-LD device 100, etc.

[0034] The reference resonator 5 is not limited to being composed of a first mirror 51 and a second mirror 52, but may include three or more mirrors. For example, the reference resonator 5 may include mirrors arranged in a V-shape or a bowtie shape. The reference resonator 5 may also include an etalon. When the reference resonator 5 includes an etalon, the front side, i.e., the side where the condenser lens 12 is located, corresponds to the first mirror 51, and the back side, i.e., the side opposite the side where the condenser lens 12 is located, corresponds to the second mirror 52. The first mirror 51 and the second mirror 52 of this etalon may form a confocal resonator. Note that the reference resonator 5 is not limited to a confocal resonator. The first mirror 51 and the second mirror 52 are not limited to concave mirrors, but may be two or more opposing flat mirrors, etc.

[0035] As described above, the SIL-LD device 100 includes the semiconductor laser light source 4 and the reference resonator 5. As described above, the optical frequency of the laser light M1 emitted from the semiconductor laser light source 4 is filtered by the reference resonator 5. This filtered light, which has a narrower linewidth than the original linewidth, is optically fed back to the semiconductor laser light source 4. As a result of the optical feedback, the laser light M1 is self-injection locked, and the linewidth of the laser light M1 is narrowed to a predetermined linewidth.

[0036] The optical path length Lb of the resonator, which is formed by the first end face 41 of the semiconductor laser light source 4 and the first surface 511 of the first mirror 51 and is necessary for optical feedback, corresponds to the sum of lengths Lb1 and Lb2. In the example shown in FIG. 1 , this is the sum of lengths Lb1 and Lb2. Length Lb1 is the length corresponding to the distance from the first end face 41 of the semiconductor laser light source 4 to approximately the center of the beam splitter 10. Length Lb2 is the length corresponding to the distance from approximately the center of the beam splitter 10 to the first surface 511 of the first mirror 51 in the reference resonator 5.

[0037] The first surface 511 of the first mirror 51 facing the second mirror 52 has a configuration common to both the optical path length Lb and the resonator length Lc.

[0038] (First cover 7) The first cover 7 covers the semiconductor laser light source 4 and the reference resonator 5, and is in contact with the first base plate 1. This brings the first cover 7 into thermal contact with the first base plate 1, and when the semiconductor laser light source 4 is driven, the temperature of the first cover 7 becomes close to the temperature of the first base plate 1. Therefore, because the semiconductor laser light source 4 and the reference resonator 5 are disposed inside the space surrounded by the first cover 7 and the first base plate 1, environmental changes are unlikely to occur inside this space, and the semiconductor laser light source 4 and the reference resonator 5 are less susceptible to the effects of environmental changes.

[0039] Furthermore, sealing with the first cover 7 makes it easier to stabilize the environment of the space sealed by the first cover 7, and extends the time over which the frequency can be maintained after the laser light M1 is resonated with the reference resonator 5. The semiconductor laser light source 4 and the reference resonator 5 are sealed by the first base plate 1 and the first cover 7. For example, the first cover 7 may effectively seal the semiconductor laser light source 4 and the reference resonator 5 by disposing an O-ring or a gasket between the first cover 7 and the first base plate 1.

[0040] When the semiconductor laser light source 4 is driven and the temperature of the first base plate 1 is kept constant, the absolute value of the difference between the temperature of the first cover 7 and the temperature of the first base plate 1 may be, for example, greater than 0°C and less than 1°C, preferably greater than 0°C and less than 0.1°C, and more preferably greater than 0°C and less than 0.001°C. The first cover 7 may be fixed to the first base plate 1 with screws. The screws may be fastened, for example, via the side wall of the first cover 7. The first cover 7 may be welded to the first base plate 1 or may be bonded with an adhesive. Considering ease of maintenance, it is preferable that the first cover 7 be fixed to the first base plate 1 with screws. The size and shape of the first cover 7 can be determined as appropriate. In the example shown in FIG. 2 , the laser light M2 transmitted through the beam splitter 10 passes through a first opening 71 provided in the first cover 7 and is emitted from the inside to the outside of the first cover 7. The material of the first cover 7 includes aluminum or copper. Heat from the first base plate 1 is efficiently transferred to the first cover 7, making it easier to bring the temperature of the first cover 7 closer to that of the first base plate 1. The first cover 7 may be made of a composite material in which a heat insulating material such as foamed resin is attached to the outside of aluminum or copper. This can reduce the influence of the temperature outside the first cover 7. The first opening 71 may be closed with a translucent member 710 such as synthetic quartz.

[0041] (Second Cover 8) The second cover 8 covers the first cover 7 and contacts the second base plate 2. The second cover 8 may be fixed to the second base plate 2 with screws. The screws are fastened, for example, through the side walls of the second cover 8. The second cover 8 may be welded to the second base plate 2 or may be bonded with an adhesive. Considering ease of maintenance, it is preferable that the second cover 8 be fixed to the second base plate 2 with screws. The second cover 8 protects the first cover 7 and the first base plate 1 from the environment outside the SIL-LD device 100. This further stabilizes the environment of the space surrounded by the first cover 7 and the first base plate 1. The size and shape of the second cover 8 can be determined as appropriate. The laser light M2 transmitted through the optical isolator 11 passes through a second opening 81 provided in the second cover 8 and is emitted as laser light Mo from the inside to the outside of the second cover 8. The material of the second cover 8 includes aluminum or copper. The second cover 8 may be made of a composite material to which a heat insulating material is further attached, similar to the first cover 7. The second opening 81 may be closed with a light-transmitting member 810 such as synthetic quartz.

[0042] The first cover 7 covers components that contribute to determining the optical path length Lb and the resonator length Lc. Meanwhile, the second cover 8 covers the first cover 7 and components that control the self-injection-locked laser light. This reduces the number and volume of components covered by the first cover 7, allowing the first cover 7 to be made smaller. The smaller first cover 7 reduces temperature unevenness in the first cover 7 and the temperature difference between the first cover 7 and the first base plate 1.

[0043] (First Collimating Lens 9) The first collimating lens 9 can be made of various types of lenses, such as a spherical lens or an aspherical lens. The first collimating lens 9 may be made of a combination of two or more lenses. The first collimating lens 9 can be made of materials such as glass, quartz, synthetic quartz, sapphire, or translucent ceramics.

[0044] (Beam splitter 10) The beam splitter 10 can be an optical element having a predetermined reflectance and transmittance for the peak wavelength of the laser light M1 emitted from the semiconductor laser light source 4. The transmittance of the beam splitter may be, for example, 50% to 80%, or 65% to 75%. The beam splitter 10 may be a plate type or a cube type.

[0045] (Optical Isolator 11) In the example shown in FIG. 1 , the optical isolator 11 is located between the first cover 7 and the second cover 8, and is positioned on the optical path P. It can also be said that the optical isolator 11 is located outside the first cover 7 and inside the second cover 8, and is positioned on the optical path P. The optical isolator 11 has a structure in which a Faraday rotator is sandwiched between two polarizers. The optical isolator 11 may be a combination of a polarizing beam splitter and a λ / 4 wave plate. The inclusion of the optical isolator 11 in the SIL-LD device 100 can reduce the amount of laser light Mo extracted from the SIL-LD device 100 that is reflected or scattered outside the SIL-LD device 100 and returned to the SIL-LD device 100. This reduces the instability of the single-mode characteristics of the SIL-LD device 100 due to the returned light of the laser light Mo. The optical isolator 11 may be disposed outside the SIL-LD device 100, if necessary.

[0046] In addition to the optical isolator 11, various optical elements such as mirrors, lenses, beam shaping elements, electro-optical modulators, or acousto-optical modulators may be arranged in the optical path P between the first cover 7 and the second cover 8.

[0047] (Condenser lens 12) Various types of lenses such as spherical lenses and aspherical lenses can be used for the condenser lens 12. The condenser lens 12 may be configured by combining two or more lenses. The condenser lens 12 can be configured to include materials such as glass, quartz, synthetic quartz, sapphire, or translucent ceramics.

[0048] (Temperature Sensor 13) The temperature sensor 13 is embedded in the first base plate 1 and can detect the temperature of the first base plate 1. The temperature sensor 13 can include a thermistor, a thermocouple, a platinum sensor, or the like. The SIL-LD device 100 maintains the temperature of the first base plate 1 constant by controlling the operation of the temperature adjustment element 3 based on the temperature of the first base plate 1 detected by the temperature sensor 13. By maintaining the temperature of the first base plate 1 constant, the SIL-LD device 100 can reduce fluctuations in the optical path length Lb caused by thermal expansion of the first base plate 1, etc. Furthermore, the temperature sensor 13 is embedded in the first base plate 1 directly below the semiconductor laser light source 4. This allows for more accurate control of the temperature of the semiconductor laser light source 4 and reduces fluctuations in the cavity length of the semiconductor laser element caused by temperature changes.

[0049] (Photodetector 55) The photodetector 55 is disposed on the opposite side to the first mirror 51 across the fourth surface 514 of the second mirror 52 provided in the reference resonator 5. The photodetector 55 detects the signal intensity of light transmitted through the second mirror 52. When the oscillation frequency of the semiconductor laser light source 4 is close to the resonance frequency of the reference resonator 5, the laser light resonates with the reference resonator 5, and a portion of the laser light is also transmitted through the second mirror 52. By detecting this transmitted light with the photodetector 55, the operation of self-injection locking can be confirmed. The photodetector 55 may be, for example, a photodiode.

[0050] (Position Adjustment Element 21) The position adjustment element 21 is an element that moves the beam splitter 10 to adjust the optical path length Lb. The position adjustment element 21 may, for example, move the beam splitter 10 in the normal direction of the reflecting surface of the beam splitter 10. The position adjustment element 21 may, for example, be a piezoelectric element. The position adjustment element 21 is disposed directly or indirectly on the first base plate 1 so as to be able to move the beam splitter 10. The position adjustment element 21 may, for example, contain lead zirconate titanate. The position adjustment element 21 may, for example, expand and contract in the normal direction of the reflecting surface of the beam splitter 10 in response to an applied drive voltage, thereby moving the beam splitter 10 in the normal direction of the reflecting surface of the beam splitter 10. However, the actuator that moves the beam splitter 10 is not limited to a piezoelectric actuator and may be an electrostatic actuator, a thermal actuator, or the like.

[0051] <Relocking Function of SIL-LD Device 100> The SIL-LD device may deviate from the self-injection locked state due to changes in the optical path length Lb or the resonator length Lc of the reference resonator 5 caused by temperature changes inside or outside the SIL-LD device, changes in air pressure, etc. When the SIL-LD device deviates from the self-injection locked state, the linewidth of the laser light Mo extracted from the SIL-LD device 100 does not become narrower than the linewidth of the laser light M1.

[0052] The SIL-LD device 100 according to this embodiment has a relocking function that controls the SIL-LD device 100 to return to the self-injection locked state when the SIL-LD device 100 has deviated from the self-injection locked state due to a temperature change or a change in air pressure inside or outside the SIL-LD device. Specifically, in the relocking function, the SIL-LD device 100 constantly monitors the detection value of the photodetector 55 of the light transmitted through the second mirror 52. The SIL-LD device 100 detects that the SIL-LD device 100 has deviated from the self-injection locked state based on the constantly monitored detection value of the photodetector 55. When the SIL-LD device 100 deviates from the self-injection locked state, the SIL-LD device 100 controls the drive current of the semiconductor laser light source 4 or the drive voltage of the position adjustment element 21 to return the SIL-LD device 100 to the self-injection locked state. The relocking function of the SIL-LD device 100 will be described below.

[0053] (Configuration of Control Unit 150) The relock function of the SIL-LD apparatus 100 is mainly realized by a control unit included in the SIL-LD apparatus 100. FIG. 3B is a block diagram showing the hardware configuration of the control unit 150 included in the SIL-LD apparatus 100. As shown in FIG. 3B, the control unit 150 has a CPU (Central Processing Unit) 151, a ROM (Read Only Memory) 152, a RAM (Random Access Memory) 153, and an I / F (Interface) 154. These are connected to each other via a system bus B so as to be able to communicate with each other.

[0054] The control unit 150 executes various processes by executing instruction codes stored in a memory using an electronic circuit, or by using an electronic circuit designed for a specific application, to realize the functions of the control unit 150. In the example shown in Fig. 3B, the electronic circuit is a CPU 151. However, the electronic circuit may also be a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), or the like.

[0055] The CPU 151 is a computing device that controls the entire SIL-LD apparatus 100. For example, the CPU 151 uses the RAM 153 as a work area, executes processes defined by various control programs stored in the ROM 152, and outputs control commands that control various operations of the SIL-LD apparatus 100.

[0056] The I / F 154 is an interface that connects the control unit 150 to communicate with external devices or apparatuses other than the control unit 150. The external devices include a position adjustment element driver 161 that drives the position adjustment element 21, a semiconductor laser driver 162 that drives the semiconductor laser light source 4, a temperature adjustment element driver 163 that drives the temperature adjustment element 3, and a voltmeter 164 that receives a light reception signal from the photodetector 55 and outputs it as a digital voltage signal. The external device is a PC (Personal Computer) or the like other than the control unit 150.

[0057] 3C is a block diagram showing the functional configuration of the control unit 150 included in the SIL-LD device 100. As shown in FIG. 3C, the SIL-LD device 100 includes a detection value acquisition unit 171, an intensity determination unit 172, a FAST control unit 173, a stabilization time determination unit 174, a FULL control unit 175, a temperature control unit 176, and an output unit 177.

[0058] The functions of the detection value acquisition unit 171 and the output unit 177 are realized by the I / F 154 or by the CPU 151 executing processes defined by various control programs stored in the ROM 152. The functions of the intensity determination unit 172, the FAST control unit 173, the stabilization time determination unit 174, the FULL control unit 175, and the temperature control unit 176 are realized by the CPU 151 executing processes defined by various control programs stored in the ROM 152. Note that some of the functions of the control unit 150 may be realized by an external device other than the control unit 150, or may be realized by distributed processing between the control unit 150 and the external device.

[0059] The detection value acquiring unit 171 controls communication with the voltmeter 164 to receive the digital voltage signal output by the voltmeter 164. The detection value acquiring unit 171 acquires the digital voltage signal as the detection value of the photodetector 55.

[0060] The intensity determination unit 172 determines whether the detection value by the photodetector 55 acquired by the detection value acquisition unit 171 is equal to or less than a predetermined intensity threshold. When the intensity determination unit 172 determines that the detection value by the photodetector 55 is equal to or less than the intensity threshold, the SIL-LD device 100 detects that the SIL-LD device 100 has deviated from the self-injection locked state.

[0061] When the SIL-LD device 100 deviates from the self-injection locked state, the FAST control unit 173 controls the drive current of the semiconductor laser light source 4 to return the SIL-LD device 100 to the self-injection locked state again. Compared to the FULL control unit 175 described later, the FAST control unit 173 can perform control to return the SIL-LD device 100 to the self-injection locked state at high speed.

[0062] After the FAST control unit 173 executes control, the stabilization time determination unit 174 determines whether the stabilization time is equal to or less than a predetermined time threshold. Here, the stabilization time refers to the duration of a state in which the detection value of the photodetector 55 acquired by the detection value acquisition unit 171 is equal to or greater than an intensity threshold. The stabilization time determination unit 174 measures the stabilization time using, for example, the clock of the CPU 151 and compares the measured stabilization time with the time threshold to determine whether the stabilization time is equal to or less than the time threshold. If the stabilization time determination unit 174 determines that the stabilization time is equal to or less than the time threshold, the SIL-LD device 100 detects that the self-injection locking state of the SIL-LD device 100 is unstable. The fact that the self-injection locking state of the SIL-LD device 100 is unstable means that the SIL-LD device 100 is in a state in which it is likely to deviate from the self-injection locking state.

[0063] When the self-injection locking state of the SIL-LD device 100 is not stable, the FULL control unit 175 controls the drive current of the semiconductor laser light source 4 and the drive voltage of the position adjustment element 21 in order to bring the SIL-LD device 100 into a stable self-injection locking state. Compared to the above-mentioned FAST control unit 173, the FULL control unit 175 can precisely control the SIL-LD device 100 to bring it into a self-injection locking state.

[0064] The temperature control unit 176 controls the operation of the temperature adjustment element 3 and adjusts the temperature of the first base plate 1. The SIL-LD device 100 can keep the temperature of the first base plate 1 constant by using the temperature control unit 176.

[0065] The output unit 177 controls communication with each of the position adjustment element driver 161, the semiconductor laser driver 162, and the temperature adjustment element driver 163, thereby outputting each control signal. For example, the output unit 177 outputs the drive current of the semiconductor laser light source 4, which is determined by the FAST control unit 173 and the FULL control unit 175, to the semiconductor laser light source 4. The output unit 177 also outputs the drive voltage of the position adjustment element 21, which is determined by the FULL control unit 175, to the position adjustment element 21. The output unit 177 also outputs a control signal for the drive voltage of the temperature adjustment element 3, which is determined by the temperature control unit 176, to the temperature adjustment element 3.

[0066] (Processing by Control Unit 150) The processing by the control unit 150 will be described with reference to FIG. 3D.

[0067] 3D is a flowchart showing an example of processing by the control unit 150. For example, the control unit 150 starts the processing of FIG. 3D when the SIL-LD device 100 enters a self-injection locked state.

[0068] First, in step S11 , the control unit 150 causes the detection value acquisition unit 171 to acquire the detection value of the photodetector 55 via the voltmeter 164 .

[0069] Subsequently, in step S12, the control unit 150 causes the intensity determination unit 172 to determine whether the detection value by the photodetector 55 is equal to or less than a predetermined intensity threshold value.

[0070] In step S12, if it is determined that the detection value by the photodetector 55 is not below a predetermined intensity threshold (step S12, NO), the control unit 150 determines that the SIL-LD device 100 is in a stable self-injection locked state, and proceeds to step S16.

[0071] On the other hand, if it is determined in step S12 that the detected value by the photodetector 55 is equal to or less than the predetermined intensity threshold value (step S12, YES), the control unit 150 detects that the SIL-LD device 100 has deviated from the self-injection locking state. In step S13, the control unit 150 controls the drive current of the semiconductor laser light source 4 by the FAST control unit 173 to return the SIL-LD device 100 to the self-injection locking state again.

[0072] Subsequently, in step S14, the control unit 150 determines, by the stable time determination unit 174, whether or not the stable time is equal to or less than a predetermined time threshold.

[0073] If it is determined in step S14 that the stabilization time is not equal to or less than a predetermined time threshold (step S14, NO), the control unit 150 determines that the SIL-LD device 100 is in a stable self-injection locked state, and proceeds to step S16.

[0074] On the other hand, if it is determined in step S14 that the stabilization time is equal to or shorter than the predetermined time threshold (step S14, YES), the control unit 150 detects that the self-injection locking state of the SIL-LD device 100 is not yet stable. In step S15, the control unit 150 controls the drive current of the semiconductor laser light source 4 and the drive voltage of the position adjustment element 21 using the FULL control unit 175 to put the SIL-LD device 100 into the self-injection locking state again. In step S15, the drive current of the semiconductor laser light source 4 may be swept with the drive voltage of the position adjustment element 21 fixed.

[0075] The FULL control unit 175 continues to adjust the drive current of the semiconductor laser light source 4 and the drive voltage of the position adjustment element 21 until the SIL-LD device 100 reaches a stable self-injection locked state. When the SIL-LD device 100 reaches a stable self-injection locked state under the control of the FULL control unit 175, the control unit 150 proceeds to step S16.

[0076] Subsequently, in step S16, the control unit 150 determines whether or not to terminate the processing. For example, the control unit 150 determines to terminate the processing when it detects that the power of the SIL-LD apparatus 100 has been turned off. However, the termination condition of the processing by the control unit 150 is not limited to that the power of the SIL-LD apparatus 100 has been turned off. For example, the termination condition may be that an operation input instructing the control unit 150 to terminate the processing has been received via the operation unit of the SIL-LD apparatus 100, that a predetermined time has arrived, or that the control unit 150 has executed the processing a predetermined number of times.

[0077] If it is determined in step S16 that the process should be terminated (YES in step S16), the control unit 150 terminates the process. On the other hand, if it is determined in step S16 that the process should not be terminated (NO in step S16), the control unit 150 proceeds to step S11. The control unit 150 repeats the processes from step S11 onwards until it is determined in step S16 that the process should be terminated.

[0078] In this way, the control unit 150 can execute the process for realizing the relock function.

[0079] Second Embodiment A SIL-LD device according to a second embodiment will be described with reference to Figures 4 and 5. Note that the same names and symbols as those in the previously described embodiments indicate the same or similar components or configurations, and detailed descriptions thereof will be omitted as appropriate. This also applies to the following embodiments and modified examples.

[0080] Fig. 4 is a schematic top view showing an example of a SIL-LD device 100a according to the second embodiment. Fig. 5 is a schematic cross-sectional view taken along line V-V in Fig. 4. Note that in Figs. 4 and 5, arrows indicate portions of the laser beams M7 to M10 passing through the interior of the SIL-LD device 100a. Also, in Figs. 4 and 5, a broken line indicates an optical path P along which the laser beams M7 to M10 pass within the SIL-LD device 100a.

[0081] In this embodiment, the semiconductor laser light source 4 includes a DFB-LD element as the semiconductor laser element 401. The reference cavity 5 resonates with laser light M7 emitted from the second facet 42 of the semiconductor laser element 401. As shown in FIG. 5 , an anti-reflection film 410 is formed on both the first facet 41 and the second facet 42 of the semiconductor laser element 401. Laser light M8 emitted from the first facet 41 of the semiconductor laser element 401 is used as output. From another perspective, the SIL-LD device 100a according to this embodiment has a configuration in which self-injection locking is performed on the side where the second facet 42 of the semiconductor laser element 401 is located, and light is extracted on the side where the first facet 41 of the semiconductor laser element 401 is located. The above points are the main differences from the first embodiment. The SIL-LD device 100a according to this embodiment is less susceptible to environmental changes, and fluctuations in the optical path length Lb and the resonator length Lc are reduced, while reductions in the output of the laser light extracted from the SIL-LD device 100a are also reduced.

[0082] For example, if an optical element for splitting laser light, such as a beam splitter, is used to extract laser light from the SIL-LD device, a power loss occurs when the laser light is split. For example, in the SIL-LD device 100 shown in Fig. 1, a portion of the light emitted from the reference resonator 5, passes through the condenser lens 12, and then enters the beam splitter 10, but does not pass through the beam splitter 10 and return to the semiconductor laser light source 4. This causes a power loss, and the optical output of the laser light extracted from the SIL-LD device may decrease.

[0083] In this embodiment, self-injection locking is performed on the second facet 42 side of the semiconductor laser element 401 to select the wavelength of the laser beam Mo extracted from the SIL-LD device 100a and narrow the linewidth of the laser beam Mo. Then, the laser beam M8 emitted from the first facet 41 of the semiconductor laser element 401 is extracted as the laser beam Mo from the SIL-LD device 100a. This eliminates the need for a branching optical element such as a beam splitter to extract the laser beam Mo from the SIL-LD device 100a, thereby improving the optical output of the laser beam Mo extracted from the SIL-LD device 100a.

[0084] 4 and 5, the SIL-LD device 100a further includes a second collimating lens 14. The second collimating lens 14 can be any of various types of lenses, such as a spherical lens or an aspherical lens. The second collimating lens 14 may be formed by combining two or more lenses. The second collimating lens 14 can be formed from materials including glass, quartz, synthetic quartz, sapphire, or translucent ceramics.

[0085] 4 and 5, the semiconductor laser element 401 can emit laser light M8 from each of the first end face 41 and the second end face 42. The laser light M8 emitted from the first end face 41 passes through the first collimator lens 9, passes through the first opening 71 of the first cover 7, passes through the optical isolator 11, and passes through the second opening 81 of the second cover 8, and is extracted as laser light Mo from the SIL-LD device 100a.

[0086] On the other hand, the laser light M7 emitted from the second end face 42 of the semiconductor laser element 401 is transmitted through each of the second collimating lens 14 and the condenser lens 12, and then enters the reference resonator 5. The laser light M7 incident on the reference resonator 5 is reflected by each of the first mirror 51 and the second mirror 52, and resonates while traveling back and forth between the first mirror 51 and the second mirror 52. The arrows indicating the laser light M9 in FIGS. 4 and 5 represent the laser light traveling back and forth between the first mirror 51 and the second mirror 52. A portion of the laser light M9 is emitted from the reference resonator 5 in the direction where the second collimating lens 14 is located while traveling back and forth between the first mirror 51 and the second mirror 52. The laser light M10 emitted from the reference resonator 5 is transmitted through each of the condenser lens 12 and the second collimating lens 14. The laser light M10 transmitted through the condenser lens 12 and the second collimator lens 14 enters the semiconductor laser element 401, and applies feedback to the optical frequency of the laser light M8.

[0087] In the example shown in Fig. 4, the optical path length Lb between the semiconductor laser light source 4 and the reference resonator 5 is the distance between the semiconductor laser light source 4 and the reference resonator 5. Specifically, it is the distance between the second end face 42 of the semiconductor laser element 401 and the first surface 511 of the first mirror 51. The optical path length Lb represents the length of the optical feedback path in self-injection locking, as in the first embodiment. The resonator length Lc is the same as in the first embodiment.

[0088] In this example, the semiconductor laser element 401 is illustrated as extending along the X direction, but is not limited to this. The light path may be adjusted by appropriately changing the direction of emission of the laser light from the semiconductor laser element 401 and by appropriately arranging a folding mirror or the like inside or outside the package of the semiconductor laser light source 4.

[0089] Third Embodiment A SIL-LD device according to a third embodiment will be described with reference to FIGS.

[0090] (First Example) Fig. 6 is a schematic top view showing a first example of a SIL-LD device 100b according to the third embodiment. Fig. 7 is a schematic cross-sectional view taken along line VII-VII in Fig. 6. Note that in Figs. 6 and 7, arrows indicate portions of the laser beams M7 to M12 passing through the interior of the SIL-LD device 100b. Also, in Figs. 6 and 7, a broken line indicates an optical path P along which the laser beams M7 to M12 pass within the SIL-LD device 100b.

[0091] The present embodiment differs from the above-described embodiments mainly in that it further includes an optical amplifier 18, which is located between the optical isolator 11 and the second cover 8 and into which the laser light M8 that has passed through the optical isolator 11 is incident. In this embodiment, the self-injection-locked laser light M8 passes through the optical amplifier 18, thereby enabling wavelength selection and amplification of the power of the laser light M8 having a narrow linewidth.

[0092] 6 and 7 has a configuration in which self-injection locking is performed on the side where the second end face 42 of the semiconductor laser light source 4 is located, and light extraction is performed on the side where the first end face 41 of the semiconductor laser light source 4 is located, similar to the second embodiment. However, the SIL-LD device 100b may have a configuration in which both self-injection locking and light extraction are performed on the side where the first end face 41 of the semiconductor laser light source 4 is located, similar to the first embodiment.

[0093] 6 and 7, the SIL-LD device 100b has a first reflecting mirror 15 and a second reflecting mirror 16 that reflect the laser light M8 that has passed through the optical isolator 11, and a third collimating lens 17 that transmits the laser light L8 reflected by the second reflecting mirror 16. The SIL-LD device 100b also has a fourth collimating lens 19 that transmits the laser light M11 that has passed through the optical amplifier 18, and a third base plate 20 on which the third collimating lens 17, the optical amplifier 18, and the fourth collimating lens 19 are mounted.

[0094] (First Reflecting Mirror 15 and Second Reflecting Mirror 16) The first reflecting mirror 15 and the second reflecting mirror 16 are aligned so that the laser light M8 is appropriately incident on the third collimating lens 17. Each of the first reflecting mirror 15 and the second reflecting mirror 16 can be made of a material such as glass, quartz, synthetic quartz, sapphire, or translucent ceramics. The positions of the first reflecting mirror 15 and the second reflecting mirror 16 can be selected appropriately depending on the specifications of the SIL-LD device 100b. The SIL-LD device 100b does not necessarily have to include mirrors such as the first reflecting mirror 15 and the second reflecting mirror 16, and may include one or more mirrors.

[0095] (Third collimating lens 17 and fourth collimating lens 19) Various types of lenses such as spherical lenses and aspherical lenses can be used for each of the third collimating lens 17 and the fourth collimating lens 19. Each of the third collimating lens 17 and the fourth collimating lens 19 may be configured by combining two or more lenses. Each of the third collimating lens 17 and the fourth collimating lens 19 can be configured to include a material such as glass, quartz, synthetic quartz, sapphire, or translucent ceramics.

[0096] (Optical Amplifier 18) The optical amplifier 18 is located between the optical isolator 11 and the second cover 8, at a position where the laser light M8 that has passed through the optical isolator 11 is incident. The optical amplifier 18 is located outside the first cover 7 and inside the second cover 8, between the optical isolator 11 and the second cover 8, and it can also be said that the optical path P passes through the optical amplifier 18. The optical amplifier 18 can be a semiconductor optical amplifier (SOA: Semiconductor Optical Amplifier) ​​or the like. The semiconductor optical amplifier may be, for example, a nitride semiconductor, an arsenide semiconductor, or a phosphide semiconductor. The optical amplifier 18 is not limited to a semiconductor optical amplifier, and a rare-earth doped optical fiber or the like can also be used. However, when amplifying visible light such as blue laser light, it is preferable to use a semiconductor optical amplifier as the optical amplifier 18.

[0097] In this embodiment, the optical isolator 11 is disposed in the optical path between the semiconductor laser element 401 and the optical amplifier 18. The optical isolator 11 reduces the return light of the light amplified by the optical amplifier 18 to the semiconductor laser element 401, and can improve the stability of the single-mode characteristics of the SIL-LD device 100.

[0098] (Third Base Plate 20) The shape and size of the third base plate 20 can be selected as appropriate as long as it can accommodate at least the third collimating lens 17, the optical amplifier 18, the fourth collimating lens 19, etc. The material of the third base plate 20 preferably includes at least one selected from the group consisting of aluminum, copper, graphite, diamond, aluminum nitride, and Super Invar. Aluminum, copper, graphite, diamond, and aluminum nitride have high thermal conductivity and are therefore excellent at dissipating heat generated by the optical amplifier 18. Furthermore, Super Invar is resistant to thermal expansion, which reduces misalignment of the optical amplifier 18 and reduces deviation of the third collimating lens 17 from the focal position.

[0099] Second Example FIG. 8 is a schematic top view showing a second example of the SIL-LD device 100b according to the third embodiment.

[0100] The SIL-LD device 100b according to the second example shown in FIG. 8 differs from the SIL-LD device 100b according to the first example in that, like the first embodiment, the self-injection locking and the light extraction are performed on the side where the first end face 41 of the semiconductor laser light source 4 is located.

[0101] 8, similarly to the first example shown in FIGS. 6 and 7, the SIL-LD device 100b causes the laser light M8 that has passed through the optical isolator 11 to enter the optical amplifier 18 via the first reflecting mirror 15, the second reflecting mirror 16, and the third collimating lens 17. The self-injection-locked laser light M8 passes through the optical amplifier 18, whereby the wavelength is selected and the power of the laser light M8 with a narrow linewidth is amplified. The SIL-LD device 100b can extract the laser light Mo with amplified power.

[0102] [Modification 1] Next, a description will be given of Modification 1 of the SIL-LD device according to the embodiment. Fig. 9 is a schematic top view of an SIL-LD device 100c according to Modification 1.

[0103] The SIL-LD device 100c according to the first modification includes a first base 1c including a recess 22, a second base plate 2 corresponding to the second base, a temperature adjustment element 3 disposed between the first base 1c and the second base plate 2, and a semiconductor laser light source 4 disposed in the recess 22 of the first base 1c. The SIL-LD device 100c also includes a reference resonator 5 disposed in the recess 22 of the first base 1c and positioned in the optical path of the laser light M1 emitted from the semiconductor laser light source 4. The SIL-LD device 100c further includes a first cover 7 that covers the semiconductor laser light source 4 and the reference resonator 5 and is in contact with the first base 1c, and a second cover 8 that covers the first cover 7 and is in contact with the second base plate 2.

[0104] 9, the first substrate 1c includes a bottom surface 221, a first side surface 222, a second side surface 223, and an upper surface 224. The recess 22 is defined by at least the bottom surface 221, the first side surface 222, and the second side surface 223. The first substrate 1c is preferably made of a material with low thermal expansion, such as Super Invar. The first substrate 1c may be made of the same material as the first base plate 1 described in the SIL-LD device 100 according to the first embodiment.

[0105] 9, the second substrate is illustrated as a second base plate 2, but is not limited to this. The second substrate may include a recess. The first substrate 1c and the optical isolator 11 may be disposed in the recess of the second substrate.

[0106] The semiconductor laser light source 4 and the reference resonator 5 are disposed on the bottom surface 221 of the first base 1c. The semiconductor laser light source 4 and the reference resonator 5 are sealed by the first base 1c and the first cover 7. This facilitates stabilizing the environment of the space sealed by the first cover 7, extending the time for which the frequency can be maintained after the laser light M1 is resonated with the reference resonator 5. In the example shown in FIG. 9 , a portion of the top surface 224 of the first base 1c is recessed, and an O-ring 73 is disposed in the recessed region of the top surface 224. This facilitates sealing. The first cover 7 is a flat plate-shaped member, and the bottom surface 72 of the first cover 7 is disposed facing the top surface 224 of the first base 1c via the O-ring 73. This facilitates sealing. The sealed space may be filled with dry air or an inert gas such as nitrogen or a rare gas. It may also be evacuated. This reduces the effects of external acoustic vibrations. A gasket may be used instead of the O-ring 73.

[0107] The first cover 7 is fixed to the first base 1c with screws 74. This makes it easy to remove the first cover 7, facilitating inspection and adjustment of the semiconductor laser light source 4 and the reference resonator 5. As shown in Figure 9, when the first cover 7 is fixed at a position where the screws 74 are closer to the recess 22 than the O-ring 73, it is preferable to further place an O-ring 73 between the screws 74 and the first cover 7 to improve airtightness.

[0108] The SIL-LD device 100c according to Modification 1 also provides the same effects as those of the SIL-LD device 100 according to the first embodiment. Note that the first base 1c and the flat plate-shaped first cover 7 in the SIL-LD device 100c are not limited to those of the SIL-LD device 100 according to the first embodiment, but can also be applied to the SIL-LD device a according to the second embodiment and the SIL-LD device b according to the third embodiment.

[0109] <Experimental Results> In the SIL-LD device 100c in which the semiconductor laser light source 4 and the reference resonator 5 are hermetically sealed with the first cover 7 and the first base 1c, the laser light and the reference resonator 5 resonated with each other, and it was possible to continue outputting a laser beam with a narrow linewidth for approximately 80 hours. In the SIL-LD device 100 in which the first cover 7 was not hermetically sealed, the laser light and the reference resonator 5 resonated with each other, and it was possible to continue outputting a laser beam with a narrow linewidth for several hours. Therefore, it was confirmed that hermetic sealing enables more stable operation.

[0110] [Modification 2] Next, a description will be given of a modification 2 of the SIL-LD apparatus according to the embodiment. Fig. 10 is a schematic top view of a SIL-LD apparatus 100d according to the modification 2.

[0111] The SIL-LD device 100d according to the second modification differs from the SIL-LD device 100c according to the first modification in that the screw 74 is fixed at a position farther from the recess 22 than the O-ring 73. This makes it possible to more easily achieve airtight sealing without providing the O-ring 73 between the screw 74 and the first cover 7. In other respects, the SIL-LD device 100d is similar to the SIL-LD device 100c according to the first modification.

[0112] [Fourth Embodiment] A molecular information output device 200 according to a fourth embodiment will be described with reference to Fig. 11. Fig. 11 is a schematic top view showing a part of the molecular information output device 200 according to the fourth embodiment.

[0113] In this embodiment, the molecular information output device 200 has a molecule S to be detected sealed between a first mirror 51 and a second mirror 52 that form the reference resonator 5 of the SIL-LD devices 100, 100a, and 100b described in the first to third embodiments. The other components are common to the SIL-LD devices 100, 100a, and 100b, and are therefore omitted to simplify the drawing. In the molecular information output device 200, a photodetector 55 that receives light transmitted through the reference resonator 5 is used to check the operation of self-injection locking, and also outputs information about the molecule S.

[0114] The molecular information output device 200 can acquire and output information about molecules S with ultra-high sensitivity through electromagnetic interactions between high-intensity, narrow-linewidth laser light accumulated in the reference resonator 5 during self-injection locking operation and molecules S in the resonator. The first cover 7 can also maintain the state of molecules S stable, improving measurement accuracy. The molecules S are, for example, gas molecules. However, the molecules S may also be molecules other than gases, such as liquids. Information about the molecules S, such as information 210 about the molecules S, including the concentration, absorbance, temperature, composition, and isotope ratio of the molecules S, can be obtained, for example, through an electrical signal output by a photodetector 55 that receives the laser light Ma1 extracted from the reference resonator 5. From the perspective of increasing the accuracy of the information 210 about the molecules S, it is preferable that the reference resonator 5 have as high a Q factor as possible.

[0115] The photodetector 55 outputs a light reception signal of the laser light Ma1 extracted from the reference resonator 5 as information 210 about the molecule S. The photodetector 55 may be a photodiode or the like.

[0116] Although the preferred embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0117] All ordinal numbers, quantitative numbers, and other figures used in the description of the embodiments are provided as examples to specifically explain the technology of the present disclosure, and the present disclosure is not limited to the illustrated figures. Furthermore, the connection relationships between components are provided as examples to specifically explain the technology of the present disclosure, and do not limit the connection relationships that realize the functions of the present disclosure.

[0118] The SIL-LD device of the present disclosure can extract laser light with a narrow linewidth, and therefore can be suitably used as a light source for molecular information output devices, analytical devices, various optical devices, etc. One suitable application example is wavelength conversion using a nonlinear optical crystal.

[0119] Aspects of the present disclosure include the following configurations. <Item 1> A self-injection locked laser device including a first base plate, a second base plate, a temperature adjustment element disposed between the first base plate and the second base plate, a semiconductor laser light source disposed on the first base plate, a reference resonator disposed on the first base plate, positioned in an optical path of laser light emitted from the semiconductor laser light source, including at least a first mirror and a second mirror, and providing optical feedback to the semiconductor laser light source, a first cover covering the semiconductor laser light source and the reference resonator and in contact with the first base plate, and a second cover covering the first cover and in contact with the second base plate. <Item 2> The self-injection locked laser device according to <Item 1>, wherein the temperature adjustment element includes a Peltier element. <Item 3> The self-injection locked laser device according to <Item 1> or <Item 2>, wherein a temperature sensor is embedded in the first base plate. <Item 4> The self-injection locked laser device according to any one of <Item 1> to <Item 3>, wherein the material of the first base plate and the second base plate includes at least one selected from the group consisting of aluminum, copper, graphite, diamond, aluminum nitride, super invar, and low thermal expansion glass. <Item 5> The self-injection locked laser device according to any one of <Item 1> to <Item 4>, wherein the material of the first cover includes aluminum or copper. <Item 6> The self-injection locked laser device according to any one of <Item 1> to <Item 5>, wherein the semiconductor laser light source includes a distributed feedback laser element. <Item 7> The self-injection locked laser device according to <Item 6>, wherein the distributed feedback laser element has a first end face and a second end face opposite to the first end face, the reference cavity resonates with laser light emitted from the second end face, and the laser light emitted from the first end face is used as an output. <Item 8> The self-injection locked laser device according to any one of <Item 1> to <Item 7>, wherein the semiconductor laser light source and the reference resonator are sealed by the first base plate and the first cover.<Item 9> A self-injection locked laser device comprising: a first base including a recess; a second base; a temperature adjustment element disposed between the first base and the second base; a semiconductor laser light source disposed in the recess of the first base; a reference resonator disposed in the recess of the first base and positioned in an optical path of laser light emitted from the semiconductor laser light source, the reference resonator including at least a first mirror and a second mirror and providing optical feedback to the semiconductor laser light source; a first cover covering the semiconductor laser light source and the reference resonator and in contact with the first base; and a second cover covering the first cover and in contact with the second base. <Item 10> The self-injection locked laser device according to <Item 9>, wherein the semiconductor laser light source and the reference resonator are sealed by the first base and the first cover. <Item 11> The self-injection locked laser device according to any one of <Items 1> to <Item 10>, further comprising an optical isolator positioned between the first cover and the second cover and positioned in the optical path. <Item 12> The self-injection locked laser device according to <Item 11>, further comprising an optical amplifier located between the optical isolator and the second cover, into which laser light that has passed through the optical isolator is incident. <Item 13> The molecular information output device according to any one of <Item 1> to <Item 12>, further comprising a molecule to be detected in the reference resonator.

[0120] This application claims priority based on Japanese Patent Application No. 2023-214224 filed with the Japan Patent Office on December 19, 2023, and includes the entire contents of this Japanese patent application.

[0121] REFERENCE SIGNS LIST 1 First base plate 1c First base body 2 Second base plate 3 Temperature adjustment element 4 Semiconductor laser light source 41 First end face 42 Second end face 401 Semiconductor laser element 402 Package 410 Anti-reflection film 420 High-reflection film 5 Reference resonator 51 First mirror 511 First surface 512 Second surface 513 Third surface 514 Fourth surface 52 Second mirror 55 Photodetector 7 First cover 71 First opening 710 Light-transmitting member 73 O-ring 74 Screw 8 Second cover 81 Second opening 810 Light-transmitting member 9 First collimating lens 10 Beam splitter 11 Optical isolator 12 Condenser lens 13 Temperature sensor 14 Second collimating lens 15 First reflecting mirror 16 Second reflecting mirror 17 Third collimating lens 18 Optical amplifier 19 Fourth collimator lens 20 Third base plate 21 Position adjustment element 100, 100a, 100b, 100c, 100d Self-injection locked laser device 150 Control unit 151 CPU 152 ROM 153 RAM 154 I / F 161 Position adjustment element driver 162 Semiconductor laser driver 163 Temperature adjustment element driver 164 Voltmeter 171 Detection value acquisition unit 172 Intensity determination unit 173 FAST control unit 174 Stabilization time determination unit 175 FULL control unit 176 Temperature control unit 200 Molecular information output device 210 Information about molecule B System bus C Central axis Lc Resonator length of reference resonator Lb Optical path length Lb1, Lb2 Length Mo, M1 to M11, Ma1 Laser light P Optical path S Molecule

Claims

1. A self-injection locked laser device comprising: a first base plate; a second base plate; a temperature adjustment element disposed between the first base plate and the second base plate; a semiconductor laser light source disposed on the first base plate; a reference resonator disposed on the first base plate and positioned in an optical path of laser light emitted from the semiconductor laser light source, the reference resonator including at least a first mirror and a second mirror, and providing optical feedback to the semiconductor laser light source; a first cover covering the semiconductor laser light source and the reference resonator and in contact with the first base plate; and a second cover covering the first cover and in contact with the second base plate.

2. The self-injection locked laser device according to claim 1, wherein said temperature adjustment element includes a Peltier element.

3. A self-injection locked laser device according to claim 1 or 2, wherein a temperature sensor is embedded in the first base plate.

4. A self-injection-locked laser device according to any one of claims 1 to 3, wherein the material of the first base plate and the second base plate includes at least one selected from the group consisting of aluminum, copper, graphite, diamond, aluminum nitride, super invar, and low thermal expansion glass.

5. A self-injection-locked laser device according to any one of claims 1 to 4, wherein the material of the first cover includes aluminum or copper.

6. A self-injection locked laser device according to any one of claims 1 to 5, wherein the semiconductor laser light source includes a distributed feedback laser element.

7. The self-injection locked laser device according to claim 6, wherein the distributed feedback laser element has a first end face and a second end face opposite to the first end face, the reference resonator resonates with the laser light emitted from the second end face, and the laser light emitted from the first end face is used as an output.

8. A self-injection locked laser device according to any one of claims 1 to 7, wherein the semiconductor laser light source and the reference resonator are sealed by the first base plate and the first cover.

9. A self-injection locked laser device comprising: a first base including a recess; a second base; a temperature adjustment element disposed between the first base and the second base; a semiconductor laser light source disposed in the recess of the first base; a reference resonator disposed in the recess of the first base and positioned in an optical path of laser light emitted from the semiconductor laser light source, including at least a first mirror and a second mirror, and providing optical feedback to the semiconductor laser light source; a first cover covering the semiconductor laser light source and the reference resonator and in contact with the first base; and a second cover covering the first cover and in contact with the second base.

10. A self-injection locked laser device according to claim 9, wherein said semiconductor laser light source and said reference resonator are sealed by said first base and said first cover.

11. The self-injection locked laser device according to any one of claims 1 to 10, further comprising an optical isolator located between said first cover and said second cover and located in said optical path.

12. The self-injection locked laser device according to claim 11, further comprising an optical amplifier located between said optical isolator and said second cover, into which the laser light that has passed through said optical isolator is input.

13. A molecular information output device comprising: a self-injection locked laser device as defined in any one of claims 1 to 12, wherein a molecule to be detected is sealed between the first mirror and the second mirror; and a photodetector that receives the laser light extracted from the reference resonator and outputs information about the molecule.

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